Communication techniques have been proposed, evaluated, and deployed to avoid or reduce the interference between two or more communication signals. For example, time division, frequency division, and code division multiplexing of signals organize transmissions in such a way that simultaneously transmitted signals use disjointed time intervals, disjointed frequency ranges, or are subject to multiplication with orthogonal signals.
Additionally, communication in many wireless systems is organized using the concept of cells. Signals in one cell use low power signals that minimally interfere with signals in other cells. The communication between the cells is conducted using a network infrastructure that operates using either optical fiber or different broadcast frequency ranges. While this technique is highly effective in sparsely populated areas, there are numerous technical difficulties when applied in densely populated places, such business headquarters, convention centers, hotels, universities, and sports facilities.
Interestingly, in the last two decades, controlled interference between wireless signals has emerged as a powerful technique for increasing wireless bandwidth, while at the same time keeping the emitted power constant through the concept of multiple input multiple output (MIMO) wireless communication systems.